ll_test.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This linked list is used to test freelist implementation.
package freelist_test

import (
	"container/list"
	"testing"

	"github.com/Snawoot/freelist"
)

// Element is an element of a linked list.
type Element struct {
	// Next and previous pointers in the doubly-linked list of elements.
	// To simplify the implementation, internally a list l is implemented
	// as a ring, such that &l.root is both the next element of the last
	// list element (l.Back()) and the previous element of the first list
	// element (l.Front()).
	next, prev *Element

	// The list to which this element belongs.
	list *List

	// The value stored with this element.
	Value any
}

// Next returns the next list element or nil.
func (e *Element) Next() *Element {
	if p := e.next; e.list != nil && p != &e.list.root {
		return p
	}
	return nil
}

// Prev returns the previous list element or nil.
func (e *Element) Prev() *Element {
	if p := e.prev; e.list != nil && p != &e.list.root {
		return p
	}
	return nil
}

// List represents a doubly linked list.
// The zero value for List is an empty list ready to use.
type List struct {
	root Element // sentinel list element, only &root, root.prev, and root.next are used
	len  int     // current list length excluding (this) sentinel element
	fl   freelist.Freelist[Element]
}

// Init initializes or clears list l.
func (l *List) Init() *List {
	l.root.next = &l.root
	l.root.prev = &l.root
	l.len = 0
	l.fl.Clear()
	return l
}

// New returns an initialized list.
func New() *List { return new(List).Init() }

// Len returns the number of elements of list l.
// The complexity is O(1).
func (l *List) Len() int { return l.len }

// Cap returns the number of preallocated elements in the freelist.
func (l *List) Cap() int { return l.fl.Cap() }

// Grow grows the freelist's capacity to guarantee space for another n elements.
// After Grow(n), at least n elements can be added to the
// list without another allocation.
// If n is negative, Grow will panic.
func (l *List) Grow(n int) {
	l.lazyInit()
	l.fl.Grow(n)
}

// Front returns the first element of list l or nil if the list is empty.
func (l *List) Front() *Element {
	if l.len == 0 {
		return nil
	}
	return l.root.next
}

// Back returns the last element of list l or nil if the list is empty.
func (l *List) Back() *Element {
	if l.len == 0 {
		return nil
	}
	return l.root.prev
}

// lazyInit lazily initializes a zero List value.
func (l *List) lazyInit() {
	if l.root.next == nil {
		l.Init()
	}
}

// insert inserts e after at, increments l.len, and returns e.
func (l *List) insert(e, at *Element) *Element {
	e.prev = at
	e.next = at.next
	e.prev.next = e
	e.next.prev = e
	e.list = l
	l.len++
	return e
}

// insertValue is a convenience wrapper for insert(&Element{Value: v}, at).
func (l *List) insertValue(v any, at *Element) *Element {
	newElem := l.fl.Alloc()
	newElem.Value = v
	return l.insert(newElem, at)
}

// remove removes e from its list, decrements l.len
func (l *List) remove(e *Element) {
	e.prev.next = e.next
	e.next.prev = e.prev
	l.fl.Free(e)
	l.len--
}

// move moves e to next to at.
func (l *List) move(e, at *Element) {
	if e == at {
		return
	}
	e.prev.next = e.next
	e.next.prev = e.prev

	e.prev = at
	e.next = at.next
	e.prev.next = e
	e.next.prev = e
}

// Remove removes e from l if e is an element of list l.
// It returns the element value e.Value.
// The element must not be nil.
func (l *List) Remove(e *Element) any {
	value := e.Value
	if e.list == l {
		// if e.list == l, l must have been initialized when e was inserted
		// in l or l == nil (e is a zero Element) and l.remove will crash
		l.remove(e)
	}
	return value
}

// PushFront inserts a new element e with value v at the front of list l and returns e.
func (l *List) PushFront(v any) *Element {
	l.lazyInit()
	return l.insertValue(v, &l.root)
}

// PushBack inserts a new element e with value v at the back of list l and returns e.
func (l *List) PushBack(v any) *Element {
	l.lazyInit()
	return l.insertValue(v, l.root.prev)
}

// InsertBefore inserts a new element e with value v immediately before mark and returns e.
// If mark is not an element of l, the list is not modified.
// The mark must not be nil.
func (l *List) InsertBefore(v any, mark *Element) *Element {
	if mark.list != l {
		return nil
	}
	// see comment in List.Remove about initialization of l
	return l.insertValue(v, mark.prev)
}

// InsertAfter inserts a new element e with value v immediately after mark and returns e.
// If mark is not an element of l, the list is not modified.
// The mark must not be nil.
func (l *List) InsertAfter(v any, mark *Element) *Element {
	if mark.list != l {
		return nil
	}
	// see comment in List.Remove about initialization of l
	return l.insertValue(v, mark)
}

// MoveToFront moves element e to the front of list l.
// If e is not an element of l, the list is not modified.
// The element must not be nil.
func (l *List) MoveToFront(e *Element) {
	if e.list != l || l.root.next == e {
		return
	}
	// see comment in List.Remove about initialization of l
	l.move(e, &l.root)
}

// MoveToBack moves element e to the back of list l.
// If e is not an element of l, the list is not modified.
// The element must not be nil.
func (l *List) MoveToBack(e *Element) {
	if e.list != l || l.root.prev == e {
		return
	}
	// see comment in List.Remove about initialization of l
	l.move(e, l.root.prev)
}

// MoveBefore moves element e to its new position before mark.
// If e or mark is not an element of l, or e == mark, the list is not modified.
// The element and mark must not be nil.
func (l *List) MoveBefore(e, mark *Element) {
	if e.list != l || e == mark || mark.list != l {
		return
	}
	l.move(e, mark.prev)
}

// MoveAfter moves element e to its new position after mark.
// If e or mark is not an element of l, or e == mark, the list is not modified.
// The element and mark must not be nil.
func (l *List) MoveAfter(e, mark *Element) {
	if e.list != l || e == mark || mark.list != l {
		return
	}
	l.move(e, mark)
}

// PushBackList inserts a copy of another list at the back of list l.
// The lists l and other may be the same. They must not be nil.
func (l *List) PushBackList(other *List) {
	l.lazyInit()
	for i, e := other.Len(), other.Front(); i > 0; i, e = i-1, e.Next() {
		l.insertValue(e.Value, l.root.prev)
	}
}

// PushFrontList inserts a copy of another list at the front of list l.
// The lists l and other may be the same. They must not be nil.
func (l *List) PushFrontList(other *List) {
	l.lazyInit()
	for i, e := other.Len(), other.Back(); i > 0; i, e = i-1, e.Prev() {
		l.insertValue(e.Value, &l.root)
	}
}

func checkListLen(t *testing.T, l *List, len int) bool {
	if n := l.Len(); n != len {
		t.Errorf("l.Len() = %d, want %d", n, len)
		return false
	}
	return true
}

func checkListPointers(t *testing.T, l *List, es []*Element) {
	root := &l.root

	if !checkListLen(t, l, len(es)) {
		return
	}

	// zero length lists must be the zero value or properly initialized (sentinel circle)
	if len(es) == 0 {
		if l.root.next != nil && l.root.next != root || l.root.prev != nil && l.root.prev != root {
			t.Errorf("l.root.next = %p, l.root.prev = %p; both should both be nil or %p", l.root.next, l.root.prev, root)
		}
		return
	}
	// len(es) > 0

	// check internal and external prev/next connections
	for i, e := range es {
		prev := root
		Prev := (*Element)(nil)
		if i > 0 {
			prev = es[i-1]
			Prev = prev
		}
		if p := e.prev; p != prev {
			t.Errorf("elt[%d](%p).prev = %p, want %p", i, e, p, prev)
		}
		if p := e.Prev(); p != Prev {
			t.Errorf("elt[%d](%p).Prev() = %p, want %p", i, e, p, Prev)
		}

		next := root
		Next := (*Element)(nil)
		if i < len(es)-1 {
			next = es[i+1]
			Next = next
		}
		if n := e.next; n != next {
			t.Errorf("elt[%d](%p).next = %p, want %p", i, e, n, next)
		}
		if n := e.Next(); n != Next {
			t.Errorf("elt[%d](%p).Next() = %p, want %p", i, e, n, Next)
		}
	}
}

func TestList(t *testing.T) {
	l := New()
	checkListPointers(t, l, []*Element{})

	// Single element list
	e := l.PushFront("a")
	checkListPointers(t, l, []*Element{e})
	l.MoveToFront(e)
	checkListPointers(t, l, []*Element{e})
	l.MoveToBack(e)
	checkListPointers(t, l, []*Element{e})
	l.Remove(e)
	checkListPointers(t, l, []*Element{})

	// Bigger list
	e2 := l.PushFront(2)
	e1 := l.PushFront(1)
	e3 := l.PushBack(3)
	e4 := l.PushBack("banana")
	checkListPointers(t, l, []*Element{e1, e2, e3, e4})

	l.Remove(e2)
	checkListPointers(t, l, []*Element{e1, e3, e4})

	l.MoveToFront(e3) // move from middle
	checkListPointers(t, l, []*Element{e3, e1, e4})

	l.MoveToFront(e1)
	l.MoveToBack(e3) // move from middle
	checkListPointers(t, l, []*Element{e1, e4, e3})

	l.MoveToFront(e3) // move from back
	checkListPointers(t, l, []*Element{e3, e1, e4})
	l.MoveToFront(e3) // should be no-op
	checkListPointers(t, l, []*Element{e3, e1, e4})

	l.MoveToBack(e3) // move from front
	checkListPointers(t, l, []*Element{e1, e4, e3})
	l.MoveToBack(e3) // should be no-op
	checkListPointers(t, l, []*Element{e1, e4, e3})

	e2 = l.InsertBefore(2, e1) // insert before front
	checkListPointers(t, l, []*Element{e2, e1, e4, e3})
	l.Remove(e2)
	e2 = l.InsertBefore(2, e4) // insert before middle
	checkListPointers(t, l, []*Element{e1, e2, e4, e3})
	l.Remove(e2)
	e2 = l.InsertBefore(2, e3) // insert before back
	checkListPointers(t, l, []*Element{e1, e4, e2, e3})
	l.Remove(e2)

	e2 = l.InsertAfter(2, e1) // insert after front
	checkListPointers(t, l, []*Element{e1, e2, e4, e3})
	l.Remove(e2)
	e2 = l.InsertAfter(2, e4) // insert after middle
	checkListPointers(t, l, []*Element{e1, e4, e2, e3})
	l.Remove(e2)
	e2 = l.InsertAfter(2, e3) // insert after back
	checkListPointers(t, l, []*Element{e1, e4, e3, e2})
	l.Remove(e2)

	// Check standard iteration.
	sum := 0
	for e := l.Front(); e != nil; e = e.Next() {
		if i, ok := e.Value.(int); ok {
			sum += i
		}
	}
	if sum != 4 {
		t.Errorf("sum over l = %d, want 4", sum)
	}

	// Clear all elements by iterating
	var next *Element
	for e := l.Front(); e != nil; e = next {
		next = e.Next()
		l.Remove(e)
	}
	checkListPointers(t, l, []*Element{})
}

func checkList(t *testing.T, l *List, es []any) {
	if !checkListLen(t, l, len(es)) {
		return
	}

	i := 0
	for e := l.Front(); e != nil; e = e.Next() {
		le := e.Value.(int)
		if le != es[i] {
			t.Errorf("elt[%d].Value = %v, want %v", i, le, es[i])
		}
		i++
	}
}

func TestExtending(t *testing.T) {
	l1 := New()
	l2 := New()

	l1.PushBack(1)
	l1.PushBack(2)
	l1.PushBack(3)

	l2.PushBack(4)
	l2.PushBack(5)

	l3 := New()
	l3.PushBackList(l1)
	checkList(t, l3, []any{1, 2, 3})
	l3.PushBackList(l2)
	checkList(t, l3, []any{1, 2, 3, 4, 5})

	l3 = New()
	l3.PushFrontList(l2)
	checkList(t, l3, []any{4, 5})
	l3.PushFrontList(l1)
	checkList(t, l3, []any{1, 2, 3, 4, 5})

	checkList(t, l1, []any{1, 2, 3})
	checkList(t, l2, []any{4, 5})

	l3 = New()
	l3.PushBackList(l1)
	checkList(t, l3, []any{1, 2, 3})
	l3.PushBackList(l3)
	checkList(t, l3, []any{1, 2, 3, 1, 2, 3})

	l3 = New()
	l3.PushFrontList(l1)
	checkList(t, l3, []any{1, 2, 3})
	l3.PushFrontList(l3)
	checkList(t, l3, []any{1, 2, 3, 1, 2, 3})

	l3 = New()
	l1.PushBackList(l3)
	checkList(t, l1, []any{1, 2, 3})
	l1.PushFrontList(l3)
	checkList(t, l1, []any{1, 2, 3})
}

func TestRemove(t *testing.T) {
	l := New()
	e1 := l.PushBack(1)
	e2 := l.PushBack(2)
	checkListPointers(t, l, []*Element{e1, e2})
	e := l.Front()
	l.Remove(e)
	checkListPointers(t, l, []*Element{e2})
	l.Remove(e)
	checkListPointers(t, l, []*Element{e2})
}

func TestIssue4103(t *testing.T) {
	l1 := New()
	l1.PushBack(1)
	l1.PushBack(2)

	l2 := New()
	l2.PushBack(3)
	l2.PushBack(4)

	e := l1.Front()
	l2.Remove(e) // l2 should not change because e is not an element of l2
	if n := l2.Len(); n != 2 {
		t.Errorf("l2.Len() = %d, want 2", n)
	}

	l1.InsertBefore(8, e)
	if n := l1.Len(); n != 3 {
		t.Errorf("l1.Len() = %d, want 3", n)
	}
}

func TestIssue6349(t *testing.T) {
	l := New()
	l.PushBack(1)
	l.PushBack(2)

	e := l.Front()
	l.Remove(e)
	// Retention of externally exposed Elements is out of scope for now
	if e.Value != nil {
		t.Errorf("e.value = %d, want nil", e.Value)
	}
	if e.Next() != nil {
		t.Errorf("e.Next() != nil")
	}
	if e.Prev() != nil {
		t.Errorf("e.Prev() != nil")
	}
}

func TestMove(t *testing.T) {
	l := New()
	e1 := l.PushBack(1)
	e2 := l.PushBack(2)
	e3 := l.PushBack(3)
	e4 := l.PushBack(4)

	l.MoveAfter(e3, e3)
	checkListPointers(t, l, []*Element{e1, e2, e3, e4})
	l.MoveBefore(e2, e2)
	checkListPointers(t, l, []*Element{e1, e2, e3, e4})

	l.MoveAfter(e3, e2)
	checkListPointers(t, l, []*Element{e1, e2, e3, e4})
	l.MoveBefore(e2, e3)
	checkListPointers(t, l, []*Element{e1, e2, e3, e4})

	l.MoveBefore(e2, e4)
	checkListPointers(t, l, []*Element{e1, e3, e2, e4})
	e2, e3 = e3, e2

	l.MoveBefore(e4, e1)
	checkListPointers(t, l, []*Element{e4, e1, e2, e3})
	e1, e2, e3, e4 = e4, e1, e2, e3

	l.MoveAfter(e4, e1)
	checkListPointers(t, l, []*Element{e1, e4, e2, e3})
	e2, e3, e4 = e4, e2, e3

	l.MoveAfter(e2, e3)
	checkListPointers(t, l, []*Element{e1, e3, e2, e4})
}

// Test PushFront, PushBack, PushFrontList, PushBackList with uninitialized List
func TestZeroList(t *testing.T) {
	var l1 = new(List)
	l1.PushFront(1)
	checkList(t, l1, []any{1})

	var l2 = new(List)
	l2.PushBack(1)
	checkList(t, l2, []any{1})

	var l3 = new(List)
	l3.PushFrontList(l1)
	checkList(t, l3, []any{1})

	var l4 = new(List)
	l4.PushBackList(l2)
	checkList(t, l4, []any{1})
}

// Test that a list l is not modified when calling InsertBefore with a mark that is not an element of l.
func TestInsertBeforeUnknownMark(t *testing.T) {
	var l List
	l.PushBack(1)
	l.PushBack(2)
	l.PushBack(3)
	l.InsertBefore(1, new(Element))
	checkList(t, &l, []any{1, 2, 3})
}

// Test that a list l is not modified when calling InsertAfter with a mark that is not an element of l.
func TestInsertAfterUnknownMark(t *testing.T) {
	var l List
	l.PushBack(1)
	l.PushBack(2)
	l.PushBack(3)
	l.InsertAfter(1, new(Element))
	checkList(t, &l, []any{1, 2, 3})
}

// Test that a list l is not modified when calling MoveAfter or MoveBefore with a mark that is not an element of l.
func TestMoveUnknownMark(t *testing.T) {
	var l1 List
	e1 := l1.PushBack(1)

	var l2 List
	e2 := l2.PushBack(2)

	l1.MoveAfter(e1, e2)
	checkList(t, &l1, []any{1})
	checkList(t, &l2, []any{2})

	l1.MoveBefore(e1, e2)
	checkList(t, &l1, []any{1})
	checkList(t, &l2, []any{2})
}

func BenchmarkContainerList(b *testing.B) {
	b.Run("PushFront", func(b *testing.B) {
		l := list.New()
		b.ResetTimer()
		for i := 0; i < b.N; i++ {
			l.PushFront(i)
		}
	})
	b.Run("PushPopFront", func(b *testing.B) {
		l := list.New()
		b.ResetTimer()
		for i := 0; i < b.N; i++ {
			l.PushFront(i)
		}
		for i := 0; i < b.N; i++ {
			l.Remove(l.Front())
		}
	})
	b.Run("PushPopFrontImmediate", func(b *testing.B) {
		l := list.New()
		b.ResetTimer()
		for i := 0; i < b.N; i++ {
			l.PushFront(i)
			l.Remove(l.Front())
		}
	})
}

func warmup(l *List, N int) {
	l.Grow(max(0, N-l.Cap()))
}

func BenchmarkFreelistList(b *testing.B) {
	b.Run("PushFront", func(b *testing.B) {
		l := New()
		b.ResetTimer()
		for i := 0; i < b.N; i++ {
			l.PushFront(i)
		}
	})
	b.Run("PushPopFront", func(b *testing.B) {
		l := New()
		b.ResetTimer()
		for i := 0; i < b.N; i++ {
			l.PushFront(i)
		}
		for i := 0; i < b.N; i++ {
			l.Remove(l.Front())
		}
	})
	b.Run("PushPopFrontImmediate", func(b *testing.B) {
		l := New()
		b.ResetTimer()
		for i := 0; i < b.N; i++ {
			l.PushFront(i)
			l.Remove(l.Front())
		}
	})
	b.Run("WarmedUpPushFront", func(b *testing.B) {
		l := New()
		warmup(l, b.N)
		b.ResetTimer()
		for i := 0; i < b.N; i++ {
			l.PushFront(i)
		}
	})
	b.Run("WarmedUpPushPopFront", func(b *testing.B) {
		l := New()
		warmup(l, b.N)
		b.ResetTimer()
		for i := 0; i < b.N; i++ {
			l.PushFront(i)
		}
		for i := 0; i < b.N; i++ {
			l.Remove(l.Front())
		}
	})
}

var Sink []*int

func BenchmarkBuiltinNew(b *testing.B) {
	Sink = make([]*int, 0, b.N)
	b.Cleanup(func() {
		Sink = nil
	})
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		Sink = append(Sink, new(int))
	}
}

func BenchmarkFreelistAlloc(b *testing.B) {
	Sink = make([]*int, 0, b.N)
	var m freelist.Freelist[int]
	b.Cleanup(func() {
		Sink = nil
	})
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		Sink = append(Sink, m.Alloc())
	}
}

func BenchmarkWarmedUpFreelistAlloc(b *testing.B) {
	Sink = make([]*int, 0, b.N)
	var m freelist.Freelist[int]
	m.Grow(b.N)
	b.Cleanup(func() {
		Sink = nil
	})
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		Sink = append(Sink, m.Alloc())
	}
}